1. Field of the Invention
The invention is related to the field of communications, and in particular, to communication network architectures that have diverse-distributed trunking and controlled protection schemes.
2. Description of the Prior Art
Communication networks are becoming increasingly complex and costly. Part of the complexity and cost is due to the various protection schemes that are implemented. A protection scheme specifies how the network ensures that user communications reach their destination. This protection can be implemented at different layers of the well-known Open Systems Interconnection (OSI) Reference Model.
OSI layer one is the physical layer, and layer one protection entails using a back-up physical path when the primary physical path fails. For example, if the layer one interface detects a failure of the primary physical path, then the layer one interface automatically re-routes the traffic over the back-up physical path. An example of layer one protection is SONET 4-fiber, bi-directional, line-switched ring protection. SONET systems re-route traffic from a failed work path to a protect path. SONET systems also use rings, where if both work and protect physical paths fail around one side of the ring, then traffic is re-routed to the protect path around the opposite side of the ring. Another example of layer one protection is digital cross-connect systems that make connections/disconnections to physically replace a failed trunk with a back-up trunk between switches.
OSI layer two is the data link layer, and layer two protection entails re-sending traffic that is not properly received by the switch on the receiving end of the trunk. Thus, layer two protection ensures that packets are correctly transferred from one switch to another over their connecting trunk. Examples of layer two protection include the Proprietary Network-to-Network Interface (PNNI) for ATM and Dynamic Packet Routing Service (DPRS) for FR. In cases where a trunk fails or becomes congested, layer two protection will divert the traffic to another trunk.
OSI layer three is the network layer, and layer three protection entails re-sending traffic that is not properly received by the destination. Thus, layer three protection ensures that packets are correctly transferred from source to destination over the connecting network. Examples of layer three protection include the Transmission Control Protocol (TCP) that is used with IP.
Current communication networks typically implement protection schemes at layer one, layer two, and layer three. Unfortunately, layer one protection requires significant excess bandwidth to provide the back-up physical paths—especially when SONET rings are used. The increased bandwidth leads to increased cost. The multiple protection schemes are also complex to manage as communication networks migrate closer to a mesh configuration.